Data Over Cable Service Interface Specification (DOCSIS) mainly supports implementation of transmission of an IP data packet between a computer network and a cable television network and between a cable television front end and a user.
The DOCSIS, as a main two-way broadband access technology of North America and European cable operators and China Broadcast & Television, has been widely used. Because of demands for high definition, interaction, 3D video services and broadband Internet access services and demands for cable network operation and maintenance management and energy saving and emission reduction, the DOCSIS technology is required to provide higher access rates, support more users, and have higher device integration levels. Meanwhile, with the popularization of the Ethernet passive optical network (EPON) in application markets of FTTB (Fiber to The Building)/FTTC (Fiber to The Curb)/FTTH (Fiber to The Home), the EPON is widely used in cable broadband access gradually. Cable access network fibers and coaxial cables coexist, and an innovative architecture needs to be proposed to merge technical systems of DOCSIS and PON in network evolution of cable networks in a better way. The industry has already proposed a DOCSIS EOC (Ethernet over Coax) solution, and has already done or is establishing standards.
In a network system adopting the DOCSIS EOC technology, a radio-frequency head-end device is moved down to approach a user-side device. In addition, an Optical Line Terminal (OLT) provides a data packet ingress and egress at a side of a broadband network, and uses an Ethernet passive optical network over coax physical layer (EPON over Coax PHY, EPOC) protocol stack to serve a cable leading to multiple users. In order to provide a service of a coaxial cable transmission radio-frequency signal, a Coax Media Converter (CMC) provides a bridging function from an EPON domain to a DOCSIS domain. That is, the CMC uses an embedded optical network unit (ONU) to terminate the EPON protocol, and uses a DOCSIS MAC (Media Access Control) layer and PHY (Physical Layer, physical layer) technology in a cable television modem termination system device to initiate the DOCSIS protocol.
However, when a data packet is transferred by adopting the prior art, a whole system is divided into an EPON domain and a DOCSIS domain which are independent, in which case end-to-end cannot be achieved, efficiency is low, service quality is difficult to ensure, and further, a bandwidth of the EPON is difficult to meet requirements.
In another solution, an EPON MAC layer technology and a coaxial cable Orthogonal Frequency Division Multiplexing (OFDM) physical layer technology are adopted, and the system includes an OLT, a CMC (or a CLT-coax line terminal), and a CNU. The CMC (or CLT) is a coax media conversion device, implements physical layer optical-to-electrical conversion, and converts an EPON physical layer into a coax physical layer. The Coax Network Unit (CNU) is a user-end device having a coax physical layer and an EPON MAC.
The MAC of the OLT may directly pass through the CMC, that is, the CMC does not terminate the EPON MAC, and the OLT can directly manage the CNU through the MAC layer. However, efficiency is not necessarily high when the EPON MAC is used for the coaxial channel, and the coaxial channel needs real-time channel measurement, so that it is inevitable to modify the EPON MAC.
Direct optical-to-electrical physical layer conversion in the CMC (or CLT) is very difficult. Features of an optical channel are stable, while features of a coaxial channel are unstable because of noise interferences, frequency selectivity, and cable and branch distributor features. Information transferring efficiency of the coaxial channel can be improved only if the coaxial channel adopts technologies such as channel measurement and bit loading, where channel changes and noise changes need to be detected in real time, and each available channel and the number of bits carried by the available channels are refreshed regularly.
Based on the above, when the data packet is transferred by adopting the prior art, the whole system is divided into an EPON domain and a DOCSIS domain which are independent, in which case end-to-end cannot be achieved, and efficiency is low.